1. Field of the Invention
This invention relates to a system for characterizing nuclear power plant components and, more particularly, to an automated system for determining dimensions associated with nuclear power plant components such as, for example, gaps between nuclear fuel assemblies.
2. Background of the Information
In a typical nuclear reactor, the reactor core includes a large number of elongated fuel assemblies. Conventional designs of these fuel assemblies include top and bottom nozzles, a plurality of elongated transversely spaced guide thimbles extending longitudinally between and connected at opposite ends to the nozzles, and a plurality of transverse support grids axially spaced along the guide thimbles. Each fuel assembly also includes a multiplicity of elongated fuel elements or rods. The fuel rods are transversely spaced apart from one another and from the guide thimbles. The transverse grids support the fuel rods between the top and bottom nozzles. The fuel rods each contain fissile material in the form of a plurality of generally cylindrical nuclear fuel pellets maintained in a row or stack thereof in the rod. The fuel rods are grouped together in an array which is organized so as to provide a neutron flux in the core sufficient to support a high rate of nuclear fission and, thus, the release of a large amount of energy in the form of heat.
U.S. Pat. No. 4,389,568 discloses a method for monitoring irradiated nuclear fuel using Cerenkov radiation. The Cerenkov light intensity is measured at selected interstices of nuclear fuel assemblies. Images of the fuel assemblies are recorded on video tape for subsequent off-line analysis. Alternatively, on-line digital analysis of the analog video signals is provided.
U.S. Pat. No. 5,309,486 discloses a surface flaw detection system for inspecting discrete manufactured nuclear fuel pellets. A line scan camera records a series of line scans for the pellets and the resulting values of pellet reflectivity are digitized. A threshold comparison of pixel values generates a binary map of "good" and "bad" pixels, the latter being outside of two thresholds. The binary map defines the edges of the pellet in the map. A processor checks for coincidence of the edge pixels with a nominal edge line that best fits the edge of the pellets, and finds surface and edge flaws.
A typical nuclear reactor core contains about 100 to 200 nuclear fuel assemblies which are typically about 13 feet tall with a square cross-section having 8.5 inch sides. The fuel assemblies are vertically positioned in an array within the reactor core and are subject to both twisting and leaning motions away from their intended positions in the array. The top nozzle of each of the fuel assemblies has two locator holes on the top thereof. These locator holes must be properly aligned with corresponding locator pins of a reactor vessel head. The reactor vessel head, which normally rests on top of the reactor core, is typically made of 8 inch sheet steel and weighs about 10 to 15 tons. Therefore, it is critical that the fuel assemblies are suitably inline for correctly engaging the corresponding locator pins of the reactor vessel head before "dropping the head".
It is known to manually use a measuring device, such as a ruler, on a video monitor in order to measure the distance or gap between nuclear fuel assemblies. However, such manual technique is laborious, subject to human error, and subject to cummulative errors as the various gaps are measured between all of the adjacent pairs of the fuel assemblies in the reactor core. Accordingly, there is room for improvement.